It is generally known to provide an internal combustion engine including an oil pump assembly for pumping engine oil through the engine to lubricate the engine components through various lubrication channels (also generally known as passageways and collectively referred to as the engine gallery). It is also known to provide the oil pump assembly with a device to regulate the oil pump pressure. It is generally known to regulate the discharge pressure during engine operation to satisfy the engine's oil pressure limits and to attempt to provide energy management to the oil pump.
Pumps for incompressible fluids, such as oil, are often either gear pumps or vane pumps. In environments such as automotive engine lubrication systems, these pumps will operate over a wide range of speeds, as the engine operating speed changes, resulting in the output volume and the output pressure, as the output of these pumps is generally supplied to a lubrication system which can be modeled as a fixed size orifice, of the pumps changing with their operating speed. Generally, an engine requires the lubrication oil pressure to increase from a minimum necessary pressure level to a maximum necessary pressure level as the engine operating speed increases, but the maximum necessary oil pressure is generally obtained from the pumps well before the engine reaches its maximum operating speed. Thus, the pumps will provide an oversupply of lubrication oil over a significant portion of the engine operating speed range. Known systems employ an oil pump, driven by the engine, for ensuring sufficient circulation of oil through the engine. While a deprivation of oil can result in damage to engine components, over-pressurized oil is also undesirable. For example, too high an oil pressure can destroy paper filter elements.
To prevent over-pressurized oil, it is generally known for the lubrication system to include a pressure relief valve. To control this oversupply, and the resulting over pressure which could otherwise damage engine components, constant displacement pumps in such environments are typically provided with a pressure relief valve which allows the undesired portion of the oversupplied oil to return to an oil sump or tank or back to the inlet port of the pump so that only the desired volume, and hence pressure, of fluid is supplied to the engine. The pressure relief valve is connected with the oil pump and engine to vent oil back into the oil sump (i.e., to the oil pump's suction side) when the oil pressure reaches a preset limit. One known type of pressure relief valve is disclosed in U.S. Pat. No. 6,116,272, wherein the pressure relief valve is integrated into the oil pump. The pressure relief valve includes a piston positioned within a cylindrical bore and the piston is biased in one direction by a spring. Pressurized oil from the oil pump outlet is supplied to the side of the piston opposite the spring and forces the piston against the spring. As the engine rotates faster, the oil pump also rotates faster and works harder and the oil pressure increases. As the oil pressure increases, the piston in the oil pressure relief valve moves against the spring and within the bore to a point where vents on the edges of the piston allow oil to escape back to the sump or pump. With this type of conventional oil pressure relief valve, the oil pump outlet pressure is used to determine when the oil pressure relief valve will open to internally by-pass the high pressure oil from the discharge side of the oil pump back to the suction side of the oil pump. A typical oil pressure relief valve of this type would be set to open at a preset pressure level appropriate for the particular engine and application.
Although such a conventional oil pressure relief valve is simple and reliable, the oil pump's power consumption is relatively high as it works to increase the oil pressure to the preset pressure level even though a lower oil pressure may be adequate to provide satisfactory lubrication of the engine components. A high power consumption by the oil pump equates to reduced fuel efficiency, which is a disadvantage. In one known application, an oil pressure relief valve for use in the lubrication system of an engine is controlled by both pump outlet pressure and by a pilot pressure applied to the opposite side of the piston in the pressure relief valve. The action of the pilot valve reduces the startup pressure spikes associated with known pilot-operated valves, while also permitting a fuel economy benefit. There long remains a need to continue to improve the fuel efficiency of the engine and its associated components and the vehicle. Several examples of these known systems include the systems disclosed in U.S. Patent Application publication numbers 2007/0231161 and 2010/0028171 and U.S. Pat. No. 7,775,503, the disclosures of which are incorporated herein.